Ubuntu Server 16.04のVagrant + Core OSで「Installing the ‘vagrant-ignition’ plugin」エラー

さくらVPSでVagrant & VirtualboxでCore OSを立ち上げようとしたらエラーになったので、解決策を探してみた。

結論から言うと解決できてない。
ただ、何をやったかだけメモとして残します。

Installing plugins: vagrant-ignition
Installing the 'vagrant-ignition' plugin. This can take a few minutes...
/usr/lib/ruby/2.3.0/rubygems/specification.rb:946:in `all=': undefined method `group_by' for nil:NilClass (NoMethodError)
    from /usr/lib/ruby/vendor_ruby/vagrant/bundler.rb:275:in `with_isolated_gem'
    from /usr/lib/ruby/vendor_ruby/vagrant/bundler.rb:231:in `internal_install'
    from /usr/lib/ruby/vendor_ruby/vagrant/bundler.rb:102:in `install'
    from /usr/lib/ruby/vendor_ruby/vagrant/plugin/manager.rb:62:in `block in install_plugin'
    from /usr/lib/ruby/vendor_ruby/vagrant/plugin/manager.rb:72:in `install_plugin'
    from /usr/share/vagrant/plugins/commands/plugin/action/install_gem.rb:37:in `call'
    from /usr/lib/ruby/vendor_ruby/vagrant/action/warden.rb:34:in `call'
    from /usr/lib/ruby/vendor_ruby/vagrant/action/builder.rb:116:in `call'
    from /usr/lib/ruby/vendor_ruby/vagrant/action/runner.rb:66:in `block in run'
    from /usr/lib/ruby/vendor_ruby/vagrant/util/busy.rb:19:in `busy'
    from /usr/lib/ruby/vendor_ruby/vagrant/action/runner.rb:66:in `run'
    from /usr/share/vagrant/plugins/commands/plugin/command/base.rb:14:in `action'
    from /usr/share/vagrant/plugins/commands/plugin/command/install.rb:32:in `block in execute'
    from /usr/share/vagrant/plugins/commands/plugin/command/install.rb:31:in `each'
    from /usr/share/vagrant/plugins/commands/plugin/command/install.rb:31:in `execute'
    from /usr/share/vagrant/plugins/commands/plugin/command/root.rb:56:in `execute'
    from /usr/lib/ruby/vendor_ruby/vagrant/cli.rb:42:in `execute'
    from /usr/lib/ruby/vendor_ruby/vagrant/environment.rb:268:in `cli'
    from /usr/bin/vagrant:173:in `<main>'
Installation of one or more plugins has failed. Aborting.

vagrant-ignitionをインストールすればいいのかな?と思って、

git clone https://github.com/coreos/vagrant-ignition.git

gem build vagrant-ignition.gemspec
WARNING:  description and summary are identical
WARNING:  See http://guides.rubygems.org/specification-reference/ for help
  Successfully built RubyGem
  Name: vagrant-ignition
  Version: 0.0.3
  File: vagrant-ignition-0.0.3.gem

vagrant plugin install vagrant-ignition-0.0.3.gem

Installing the 'vagrant-ignition-0.0.3.gem' plugin. This can take a few minutes...
/usr/lib/ruby/2.3.0/rubygems/specification.rb:946:in `all=': undefined method `group_by' for nil:NilClass (NoMethodError)
    from /usr/lib/ruby/vendor_ruby/vagrant/bundler.rb:275:in `with_isolated_gem'
    from /usr/lib/ruby/vendor_ruby/vagrant/bundler.rb:131:in `install_local'
    from /usr/lib/ruby/vendor_ruby/vagrant/plugin/manager.rb:47:in `install_plugin'
    from /usr/share/vagrant/plugins/commands/plugin/action/install_gem.rb:37:in `call'
    from /usr/lib/ruby/vendor_ruby/vagrant/action/warden.rb:34:in `call'
    from /usr/lib/ruby/vendor_ruby/vagrant/action/builder.rb:116:in `call'
    from /usr/lib/ruby/vendor_ruby/vagrant/action/runner.rb:66:in `block in run'
    from /usr/lib/ruby/vendor_ruby/vagrant/util/busy.rb:19:in `busy'
    from /usr/lib/ruby/vendor_ruby/vagrant/action/runner.rb:66:in `run'
    from /usr/share/vagrant/plugins/commands/plugin/command/base.rb:14:in `action'
    from /usr/share/vagrant/plugins/commands/plugin/command/install.rb:32:in `block in execute'
    from /usr/share/vagrant/plugins/commands/plugin/command/install.rb:31:in `each'
    from /usr/share/vagrant/plugins/commands/plugin/command/install.rb:31:in `execute'
    from /usr/share/vagrant/plugins/commands/plugin/command/root.rb:56:in `execute'
    from /usr/lib/ruby/vendor_ruby/vagrant/cli.rb:42:in `execute'
    from /usr/lib/ruby/vendor_ruby/vagrant/environment.rb:268:in `cli'
    from /usr/bin/vagrant:173:in `<main>'

同じエラー。

Virtualbox側がまずい?と思って、おもむろにバージョンチェックしてみると、

virtualbox -v

Qt WARNING: VirtualBox: cannot connect to X server

X serverがないと。インストールしてみます。

sudo apt-get -y install xserver-xorg x11-xserver-utils

再度チャレンジ。

virtualbox -v

Qt WARNING: VirtualBox: cannot connect to X server

ダメ。

というか、Virtualboxってデスクトップ環境なしだと動かない??